MA = "mechanical advantage," and is a measure of force multiplication provided by the lifting mechansim, in this case the pulley system. It is equal to the ratio of the weight of the carton you are lifting to the force you apply on the rope to lift it. So here MA = 225/129 = 1.744, just as you figured it.
IMA = "Ideal Mechanical Advantage," and is the mechanical advantage yuo would have under ideal conditions, meaning no losses of power and efficiency = 100%. It's determined by the physical construct of the pulley system, in this case the ratio of the amount of rope you pull to the height the carton is lifted. So IMA = 33/16.5 = 2.
Note that the actual MA is less than ideal, so the efficiency of the mechanism is less than 100%. The ratio of MA/IMA gives the efficiency, which is 1.744/2 = 87.2%. Alternatively efficiency can be calculated from the ratio of the work done on the weight being lifted to the amount of work applied done by the person pulling the rope:
Eff = (225N x 16.5)/(129N x 33m) = 87.2%
Hope this helps.
